Problem: 6 notebooks cost $9.30. Which equation would help determine the cost of 14 notebooks?
Answer: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 6 notebooks. We want to know the cost of 14 notebooks. We can write the numbers of notebooks as a proportion: $\dfrac{6}{14}$ We know 6 notebooks costs $9.30. We can let $x$ represent the unknown cost of 14 notebooks. The proportion of these costs can be expressed as: $\dfrac{\$9.30}{x}$ The cost changes along with the number of notebooks purchased, and so the two proportions are equivalent. $\dfrac{6}{14} = \dfrac{\$9.30}{x}$